1. Field of the Invention
The present invention relates to an endoscope apparatus and an illumination control method of the endoscope apparatus.
2. Description of the Related Art
For example, JP-A-2006-296656 discloses an endoscope apparatus including an illumination means for emitting laser light from a semiconductor light emitting element to a fluorescent substance so as to perform white illumination by exciting the fluorescent substance to emit light. According to this kind of endoscope apparatus, by using the laser light, it is possible to obtain high illumination light which has lower power consumption than that of a halogen lamp or xenon lamp. However, in the semiconductor light emitting element, even in a product having the same specification, there is differences in the light emission wavelength in accordance with the conditions of the manufacturing process or the materials to be used. Due to differences in the light emission wavelength, the light emission efficiency of the fluorescent substance may be reduced even by a slight difference in the wavelength in accordance with the material of the fluorescent substance. In this case, since the energy applied to the semiconductor light emitting element needs to be increased in order to obtain a predetermined light amount, needless energy loss occurs.
Particularly, in the case where the absorption spectrum of the fluorescent substance in a blue wavelength bandwidth is a rapid profile, the light emission efficiency of the fluorescent substance is increased or decreased due to a slight variation in the light emission wavelength of the semiconductor light emitting element. As a result, even when the fluorescent substance is illuminated by the same light emission intensity, the light emission intensity of the fluorescent substance is reduced, and hence bluish-white illumination is performed. Likewise, due to differences in the light emission wavelength, a difference occurs in the light emission spectrum of the white light formed by the laser light and the excitation light, and variations occur in the tone of the image, thereby causing a problem in that a correct diagnosis may be impeded.
In addition, the spectral sensitivity of the imaging element may be easily and largely deteriorated around 400 nm. In the case of using the semiconductor light emitting element having a short wavelength substantially equal to 400 nm, a slight difference in the light emission wavelength influences the light receiving sensitivity of the imaging element. For this reason, the wavelength of the light emitted from the semiconductor light emitting element needs to be maintained with high precision to be a stipulated constant value.
Further, in the manufacturing process of the semiconductor light emitting element, a product inspection step is performed after manufacturing so as to remove through inspection products which are out of the stipulated light emission wavelength range, and only products having similar quality levels are supplied to the market. Accordingly, the cost of the components of the semiconductor light emitting element tends to easily increase, which impedes a decrease in the cost of the endoscope apparatus.